﻿// ---------------------------------------------------------------------------------------------------------------------
//   Copyright (c) SRT Solutions 2009. All rights reserved.
// ---------------------------------------------------------------------------------------------------------------------

namespace SRTSolutions.Elevate
{
    using global::System.Collections.Generic;
    using global::System.Linq;

    /// <summary>
    /// An IList that is not constructed until a value is accessed.
    /// </summary>
    public class DelayedList<T> : IList<T>
    {
        private int initialCount;
        private IEnumerable<T> source;

        private IList<T> actualBackingList;

        private IList<T> BackingList
        {
            get
            {
                if (actualBackingList == null)
                {
                    actualBackingList = source.ToList();
                }

                return actualBackingList;
            }
        }

        /// <summary>
        /// Initializes a new instance of the DelayedList class.
        /// </summary>
        /// <param name="source">The source.</param>
        public DelayedList(IEnumerable<T> source)
        {
            this.source = source;
        }

        /// <summary>
        /// Initializes a new instance of the DelayedList class.
        /// </summary>
        /// <param name="source">The source.</param>
        /// <param name="initialCount">The initial count of the list.</param>
        public DelayedList(IEnumerable<T> source, int initialCount)
        {
            this.initialCount = initialCount;
            this.source = source;
        }

        #region IList<T> Members

        /// <summary>
        /// Determines the index of a specific item in the <see cref="T:System.Collections.Generic.IList`1"/>.
        /// </summary>
        /// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.IList`1"/>.</param>
        /// <returns>
        /// The index of <paramref name="item"/> if found in the list; otherwise, -1.
        /// </returns>
        public int IndexOf(T item)
        {
            return BackingList.IndexOf(item);
        }

        /// <summary>
        /// Inserts an item to the <see cref="T:System.Collections.Generic.IList`1"/> at the specified index.
        /// </summary>
        /// <param name="index">The zero-based index at which <paramref name="item"/> should be inserted.</param>
        /// <param name="item">The object to insert into the <see cref="T:System.Collections.Generic.IList`1"/>.</param>
        /// <exception cref="T:System.ArgumentOutOfRangeException">
        /// 	<paramref name="index"/> is not a valid index in the <see cref="T:System.Collections.Generic.IList`1"/>.
        /// </exception>
        /// <exception cref="T:System.NotSupportedException">
        /// The <see cref="T:System.Collections.Generic.IList`1"/> is read-only.
        /// </exception>
        public void Insert(int index, T item)
        {
            BackingList.Insert(index, item);
        }

        /// <summary>
        /// Removes the <see cref="T:System.Collections.Generic.IList`1"/> item at the specified index.
        /// </summary>
        /// <param name="index">The zero-based index of the item to remove.</param>
        /// <exception cref="T:System.ArgumentOutOfRangeException">
        /// 	<paramref name="index"/> is not a valid index in the <see cref="T:System.Collections.Generic.IList`1"/>.
        /// </exception>
        /// <exception cref="T:System.NotSupportedException">
        /// The <see cref="T:System.Collections.Generic.IList`1"/> is read-only.
        /// </exception>
        public void RemoveAt(int index)
        {
            BackingList.RemoveAt(index);
        }

        /// <summary>
        /// Gets or sets the value at the specified index.
        /// </summary>
        /// <value></value>
        public T this[int index]
        {
            get { return BackingList[index]; }
            set { BackingList[index] = value; }
        }

        #endregion

        #region ICollection<T> Members

        /// <summary>
        /// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary>
        /// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
        /// <exception cref="T:System.NotSupportedException">
        /// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
        /// </exception>
        public void Add(T item)
        {
           BackingList.Add(item);
        }

        /// <summary>
        /// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary>
        /// <exception cref="T:System.NotSupportedException">
        /// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
        /// </exception>
        public void Clear()
        {
            BackingList.Clear();
        }

        /// <summary>
        /// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"/> contains a specific value.
        /// </summary>
        /// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
        /// <returns>
        /// true if <paramref name="item"/> is found in the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false.
        /// </returns>
        public bool Contains(T item)
        {
            return BackingList.Contains(item);
        }

        /// <summary>
        /// Copies the elements of the <see cref="T:System.Collections.Generic.ICollection`1"/> to an <see cref="T:System.Array"/>, starting at a particular <see cref="T:System.Array"/> index.
        /// </summary>
        /// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from <see cref="T:System.Collections.Generic.ICollection`1"/>. The <see cref="T:System.Array"/> must have zero-based indexing.</param>
        /// <param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.</param>
        /// <exception cref="T:System.ArgumentNullException">
        /// 	<paramref name="array"/> is null.
        /// </exception>
        /// <exception cref="T:System.ArgumentOutOfRangeException">
        /// 	<paramref name="arrayIndex"/> is less than 0.
        /// </exception>
        /// <exception cref="T:System.ArgumentException">
        /// 	<paramref name="array"/> is multidimensional.
        /// -or-
        /// <paramref name="arrayIndex"/> is equal to or greater than the length of <paramref name="array"/>.
        /// -or-
        /// The number of elements in the source <see cref="T:System.Collections.Generic.ICollection`1"/> is greater than the available space from <paramref name="arrayIndex"/> to the end of the destination <paramref name="array"/>.
        /// -or-
        /// Type <typeparamref name="T"/> cannot be cast automatically to the type of the destination <paramref name="array"/>.
        /// </exception>
        public void CopyTo(T[] array, int arrayIndex)
        {
            BackingList.CopyTo(array, arrayIndex);
        }

        /// <summary>
        /// Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary>
        /// <value></value>
        /// <returns>
        /// The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </returns>
        public int Count
        {
            get { return actualBackingList == null ? initialCount : BackingList.Count; }
        }

        /// <summary>
        /// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
        /// </summary>
        /// <value></value>
        /// <returns>true if the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only; otherwise, false.
        /// </returns>
        public bool IsReadOnly
        {
            get { return false; }
        }

        /// <summary>
        /// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </summary>
        /// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
        /// <returns>
        /// true if <paramref name="item"/> was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. This method also returns false if <paramref name="item"/> is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"/>.
        /// </returns>
        /// <exception cref="T:System.NotSupportedException">
        /// The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
        /// </exception>
        public bool Remove(T item)
        {
            return BackingList.Remove(item);
        }

        #endregion

        #region IEnumerable<T> Members

        /// <summary>
        /// Returns an enumerator that iterates through the collection.
        /// </summary>
        /// <returns>
        /// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
        /// </returns>
        public IEnumerator<T> GetEnumerator()
        {
            return BackingList.GetEnumerator();
        }

        #endregion

        #region IEnumerable Members

        /// <summary>
        /// Returns an enumerator that iterates through a collection.
        /// </summary>
        /// <returns>
        /// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
        /// </returns>
        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return BackingList.GetEnumerator();
        }

        #endregion
    }
}
